Process for dissolving cellulose and reclaiming rubber



Patented Apr. 23, 1935 i v v 1,998,449

- UNITED-suresPATENT OFFICE PROCESS FOR DISSOLVING CELLULOSE AND RECLAIM'ING RUBBER Richard Lloyd Davies, Denver, 0010., assignor to Pennsylvania Salt Manufacturing Company, milelphig. Pa., a corporation of Pennsyl- No Drawing. Application January 28, 1933, Serial No. 654,105

8 Claims. (01. 18-42) This invention relates to improvements in to the presence in the rubber of the accelerator, meth ds for reclaiming and softening rubber and the rubber tends to remain in a stable cured state for dissolving the cellulose contained in rubber and the refining operation is long and costly and junk. usually amounts to from two cents to three cents Old and worn out tire casings and inner tubes P r P f r pneumatic tiies form one of the principal I'have discovered thatif the scrap is subjected sources from which rubber isreclaimed and will While in h digester t the action 0! as nt be employed for the purpose of describing oxy en. the 00s 1 h r laimin p o 0811 improved process. be greatly reduced because these elements facili- Tire casings invariably contain cott n fabric, tate the removal of the cellulose, thereby making 10 either woven or in the form of latex treated cord i P i l to pl y 350 p n f Caustic oda and in addition the rubber is nearly always mixed ead 01,500 pounds p r charge 0 P u ds with a chemi al a l t o common of scrap, and to materially decrease the amount celerator is known to th trad as mercgpto-- of oil used, which results in a substantial savbenzothiazole. ing. In addition to the saving effected in the Inner tubes are, as a general rule, free from cost of the caustic soda, the oxygen also decotton fabric, but nearly always contain an ac- Dolymerizes part of the rubber forming a viscous, celerator. resinous substance that acts as a solvent for the It is evident that in reclaiming jire a i remainder, and thus assists in softening the rubit becomes necessary to separnte the ll lo ber and reduces the time required for refining. 20

cotton fibre from the rubber nd thi is The oxygen seems also to decompose the acceleraplished by subjecting the scrap to the action of t w ic makes i possible to more i y decaustic soda, in a manner presently to be deflee-Bile the rubberscribed. The presence of the accelerator also In accordance with my imp v me t has an effect on therubber which increases th scrapis subjectedto the same treatment as before, 25 dimculty of properly softening it, and whi h t but instead of using 500 pounds of caustic soda, is one object of this invention to overcome. the amount reduced to 350 p n an 2 f In order to describe the invention and point pounds of calcium hypochlorite is'added. The out inavhat respect it diifers from the present hypeelflelite Should P f rably contain 70% of methods, one ofthe processes now employed will available chlorine. The treatmcnt'in the digester be first described. Y can now be shortened to ten hours.' After the 'Old tire casings are cut into small pieces contents of the-digests? has been washed and which will pass through three-quarterinch h dried, it is then milled or refined. but on account screen; this will be referredto as scrap. The. of the abtlon produced by the oxygen, the time re-' scrapie then put into a-steam jacketed q l l. em b I eafly decrease 35' The usual charge for a is 4500 pounds of thereby eiiecting av'considerable saving which;

. scrap. To the charge in the digester 500 pounds 'whenaddedto thesaving in the amount of'chem..:;- of caustic soda Na(OH) is now added, together icals makes a u ia w s perroundof with 200 pounds asphalt; 200 pounds pine tar; m t l flli Y v 4 40 100 pounds, oleum spirits and 7000 pounds of In clai s rubber f om tubes the p o m 40 water. The digester i now l d d t t of removing the cotton or cellulose is not present about 200 pounds per square inch, is the dand the process can therefore be varied somemitted to the jacket and this pressure maintained 1 What- The tubes. lite! h l cut into m ll Pieces, v

for the period of the treatment. The digester is are boiled with caustic soda in'an open boiler for L provided with an agitator which is operated dura period of about four hours, after which they 45 ing the period of treatment which is usually flfare treated with oil and subjected to steam pres-v teen hours. The contents of the agitator is now sur after which the rubber is washed and dried. dumped after which it is washed and dried. The Where the rubber contains the accelerator known cellulose, which has been dissolved by theaction as; mercaptobenaotliiazole itwiil' not soften under 59 of the caustic soda,'is removed with thEHQHIivfth-l,

The rubber is 'soitened to some extent by the ndeed lcsai v action of the oleum, pine tar and asphalt in conj "by to the'contents oi! ;-junction.withthe caustic soda. The dried the open bciler'anyhypochlorlte the rubber stock .teriai is now refined or milled by p it -;will' soften f'evenIiiit "the accelerator-7;}.

between rolls imtil it becomes plastic, Owing proceas' and' suchfs'crap hasheretorore so) be refined with satisfactory results. By the addition of the hypochlorite, smaller amounts of caustic soda and softening oils are required with a corresponding saving. The times required for boiling, devulcanizing and refining are also each materially shortened.

The reclaimed rubber that results when the scrap is subjected to the action of oxygen is a better rubber when considered from the standpoint of tensile strength, stretch, etc., than reclaimed rubber obtained by the old method, and therefore in addition to decreasing the cost the improved method alsoincreases the value of the product.

Instead of adding a hypochlorite to the caustic soda solution, it is possible to generate it in the digester or the boiler by introducing chlorine gas; thus, 2Na(QH +H20+C1a=NaOC1+NaC1+2H:O. In either case the oxygen is released from its chemical bonds and while in its nascent state produces the effects described. The exact quantity of hypochlorite used can be varied greatly and is determined mostly by the consideration of cost as it has been found that the eifects usually increase with the amount of hypochlorite, but it is also apparent that too great an excess will not do any good. Improved results have been obtained when as little as two pounds of hypochlorite have been added to a charge of 4500 pounds of scrap and better results when the amoimt has been increased to ten pounds and as high as twenty-five pounds. The addition of the hypochlorite increases the rate at which the cellulose is dis solved, as well as softens the rubber in spite of the effect of the accelerator. It therefore follows that the addition of hypochlcrite to caustic soda has beneficial effects wherever cellulose is to be digested, as in the production of rayon.

The exact reason for the beneficial results obtained are not positively known, but it is believed that the oxygen while in its nascent state produces a chemical action to which. the results are due.

In the above portions of this specification, at-

terials compounded in the rubber, oxygen is separated from the hypochlorite and produces an oxydizing effect on all of the materials and a depolymerizing efi'ect on the rubber, and similarly it maybe in some cases, that the reagents produce a chiorinating as well as a depolymerizing effect.

The object of depolymerizing the rubber is to increased and when carried still farther a rubber results which is lessinfiammable and more impervious to petroleum products and other rubber solvents than rubber not so treated.

In the above description hypochlorite'has been pointed out as being the most desirable member of the halogen group for the purpose under consideration, but hypobromites and hypoiodites are also efi'ective and'can be substituted for hypochlorites in the method described above with substantially the same results; it is therefore evident that the hypohaiites are equivalents and the selection is governed primarily by cost consideration.

What I claim is:

1. The method of treating rubber to produce depolymerization which comprises subjecting the rubber to the action of caustic soda and a hypochlorite.

2. The method of reclaiming rubber which comprises subjecting the rubber scrap under treatment to the action of caustic soda and a hypochlorite.

3. The method of reclaiming rubber from scrap containing rubber and cellulose which comprises subjecting the rubber scrap under treatment to the action of caustic soda and a hypochlorite.

4. The method of reclaiming rubber from scrap containing rubber and cellulose which comprises subjecting the scrap to heat and agitation while mixed with caustic soda and a chemical which will react with the caustic soda to produce a hypohalite.

5. The method of reclaiming rubber from scrap containing rubber and cellulose which comprises subjecting the scrap to heat and agitation while mixed with caustic soda and a hvpochlorite.

6. The method of treating rubber .to produce d p lymerizat-ion, which comprises subjecting the rublzgr to the action of caustic soda and a hypohali 7. The method of reclaiming rubber from scrap containing rubber and cellulose, which comprises subjecting the rubber scrap under treatment to the action of caustic soda and a hypohalite.

8. The method of reclaiming rubber from scrap containing rubber. and cellulose, which comprises subjecting the scrap to heat and agitation while mixed with caustic soda, and passing chlorine into the mixture to react with the caustic soda to produce a hypochlorite.

. RICHARD DAVIES. I 

